Stepmania 5 beta 4a crashes with Cyberia Style

I will check ffmpeg binaries as soon as I am in front of my computer. About wrong Stepmania version, I don't think I have made such a mismatch (each build has its own target directory), but I will check also.

I didn't know your building tutorial page. Since I started Stepmania a year ago, I was using this old wiki page. Strangely enough, I ended up with ./configure && make && sudo make install, although nothing in the old tutorial told me this (but well, that's a pretty common way to build stuff). I was doing like that for previous versions also, the ones which used to work, so make install did work.

There are some chances ffmpeg binaries might be mis-installed during make install process? I will check this as soon as I can. I remember I couldn't find ffmpeg in the installed application directory...

But I still think it is something related to my distro. Many people were complaining otherwise...

I just confirmed on Debian Jesse that if you use make install and run the executable it puts in /opt/stepmania-5/ it will crash when playing a video.
Don't run make install, it doesn't set up the linking with the bundled ffmpeg correctly. Just run the executable that is built in the src directory, from the top level stepmania directory like my guide explains.

Next time someone has this problem with videos, another option besides rebuilding stepmania correctly (preferred) is to set "MovieDrivers=Null" in Preferences.ini, which will disable videos entirely, and should prevent crashing.